674 A MANUAL OF VETERINARY PHYSIOLOGY 



undue wear, for the part is hard and tough, while the younger 

 and moister horn at the posterior part of the foot allows of 

 elasticity. In this way the ground surface of the foot is provided 

 with the hardest horn where fraction is greatest. In theory, no 

 fraction of an inch of the ground surface of the foot, from toe to 

 heel, is of quite the same age. 



The toe of the wall appears to grow faster than either the 

 quarters or the heels, but this is more imaginary than real ; it 

 is the tendency of the foot to grow forward as well as downward 

 which produces the illusion. That the foot grows forward may 

 readily be determined by experiment, for if a cut be made in the 

 wall at the coronet, say an inch or so from the heels, it will in 



Fig. 237. — Diagram illustrating the Age of the Wall. 



a, b, c, d, e, f, are circles drawn round the hoof parallel to the coronet ; in this 



Awav it is ascertained that, the age of the wall at a is the same as the heel at 



a' ; the age of the wall at d corresponds with the age of the quarter at d' . 



Every portion of the ground surface of the wall is of a different age, being 



oldest and hardest at/', and youngest and most elastic at a'. 



course of time be carried some considerable distance towards the ' 

 toe ; the exact amount can be determined by observing the 

 obliquity of the horn fibres. 



How the Weight is carried by the Foot. — It is universally 

 recognised that the weight of the body is supported by the 

 union of the insensitive with the sensitive laminae. That the 

 enormous weight 01 the horse's body should be carried upon — 

 or, rather, slung upon — thin delicate strips of sensitive material 

 on the one hand, and correspondingly delicate strips of horn 

 on the other, is perhaps the most remarkable feature in the 

 physiology of the foot. This union is so firm that it is a matter 

 of extreme difficulty to separate the two surfaces, even by 

 mechanical means. In a single foot the weight is carried on 600 

 or more primary laminae, assisted by 72,000 or more secondary 



